Raid-topology-aware multipath routing

ABSTRACT

Determining a preferred interface for write access to a data storage system having multiple interfaces. Interface preference is determined at the data-stripe level. Write requests are routed to the preferred interface.

BACKGROUND

The present invention relates generally to the field of storagevirtualization, and more particularly to multipath routing invirtualized storage systems.

The Wikipedia entry for “Multipath I/O”(http://en.wikipedia.org/wiki/Multipath_I/O, as of Mar. 26, 2015) statesas follows: “[M]ultipath I/O [MPIO] is a fault-tolerance andperformance-enhancement technique that defines more than one physicalpath between the CPU in a computer system and its mass-storage devices .. . . Multipath software layers can leverage the redundant paths toprovide performance-enhancing features, including dynamic loadbalancing, traffic shaping, automatic path management, and dynamicreconfiguration.” MPIO can be used, for example, with direct-attachedstorage (DAS), network-attached storage (NAS), and storage area network(SAN) storage architectures.

Multipath routing algorithms choose the path on which to send an I/Orequest from among the multiple paths between a host and a storagesubsystem. A path consists of a specific interface on the host and aspecific interface on the storage subsystem, along with zero or moreintermediate ‘hops’ which are introduced by, for example, SAN switches.Components along the path may be real or virtual. Current supportedrouting algorithms include round-robin (alternate sequentially amongpaths), queue-length (choose the path with the least number ofuncompleted I/O requests), service-time (choose the path which has theshortest estimated service time), and others.

The Wikipedia entry for “RAID” (http://en.wikipedia.org/wiki/RAID, as ofMar. 26, 2015) states as follows: “RAID (originally redundant array ofinexpensive disks; now commonly redundant array of independent disks) isa data storage virtualization technology that combines multiple diskdrive components into a logical unit for the purposes of data redundancyor performance improvement.”

Known RAID configurations include the standard levels RAID 0 throughRAID 6, nested levels, and many non-standard levels. Storage subsystemsoften support RAID. RAID is typically used in these contexts to increasethe availability or performance of storage by distributing andduplicating data over a collection of storage devices, which may be, forexample, disks or flash modules. RAID 5 is a particular form of RAID inwhich a logically contiguous fixed-size set of blocks (the “datablocks”) are distributed evenly over a set of devices and augmented by aparity block which is stored on a separate device. The logicallycontiguous set of blocks is known as a “stripe”. The contents of theparity block are calculated from the contents of the data blocks in sucha way that the original data can be reconstructed in the event of thecorruption of any single data block. Each of the data and parity blocksare stored on different devices, so that the original data can bereconstructed in case of a single device failure.

SUMMARY

According to an aspect of the present invention, there is a method,computer program product and/or system that performs the followingactions (not necessarily in the following order): (i) receives a set ofinput data; (ii) determines, based on the set of input data, a set ofstripe-interface preferences respectively between: (a) stripes of aplurality of data stripes of a data storage system, and (b) storagesystem interfaces of a plurality of storage system interfaces, with thepreferences including a first preference between a first data stripe anda first storage system interface; and (iii) routes a first request forstoring a first piece of data to the first data stripe of the datastorage system to the first storage system interface based on the firstpreference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of a system according tothe present invention;

FIG. 2 is a flowchart showing a first embodiment method performed, atleast in part, by the first embodiment system;

FIG. 3 is a block diagram showing a machine logic (for example,software) portion of the first embodiment system;

FIG. 4 is a diagram of interface write buffers showing data buffering(with block transfers between buffers of different interfaces) helpfulin understanding a second embodiment system according to the presentinvention; and

FIG. 5 is a diagram of interface write buffers showing data buffering(without block transfers between buffers of different interfaces) asoccurs in the second embodiment system.

DETAILED DESCRIPTION

Some embodiments of the present invention include a multipath routingalgorithm designed to reduce the performance degradation caused by thetransfer of RAID parity blocks between private I/O interface cachebuffers on storage subsystems that have multiple I/O interfaces.According to some embodiments of the multipath routing algorithm, apiece of data to be written to a storage system is sent to an I/Ointerface (also sometimes herein referred to as a “storage systeminterface”) that already has the parity block buffered. This DetailedDescription section is divided into the following sub-sections: (i) TheHardware and Software Environment; (ii) Example Embodiment; (iii)Further Comments and/or Embodiments; and (iv) Definitions.

I. The Hardware and Software Environment

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a set of operational actions to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

An embodiment of a possible hardware and software environment forsoftware and/or methods according to the present invention will now bedescribed in detail with reference to the Figures. FIG. 1 is afunctional block diagram illustrating various portions of file serversystem 100, including: file server computer 200; communication unit 202;processor set 204; input/output (I/O) interface set 206 containing hostbus adapter (HBA) 306; storage area network (SAN) 114; logical unit(logical unit number, or LUN) 104, which is a RAID array with disks 315,316, and 317, and is connected to SAN 114 via I/O interfaces 311 and312; memory device 208; persistent storage device 210; display device212; external device set 214; random access memory (RAM) devices 230;cache memory device 232; table 302; and program 300. Disks 315 and 316contain data blocks 321, 322, 324, and 325, while disk 317 containsparity blocks 323 and 326. Stripe 331 is composed of data blocks 321 and322 and their associated parity block 323, while stripe 332 is composedof data blocks data blocks 324 and 325 and their associated parity block326. Both stripes 331 and 332 can be written to via either of I/Ointerfaces 311 or 312.

File server computer 200 is, in many respects, representative of thevarious computer sub-system(s) in the present invention. Accordingly,several portions of computer 200 will now be discussed in the followingparagraphs.

Computer 200 may be a laptop computer, tablet computer, netbookcomputer, personal computer (PC), a desktop computer, a personal digitalassistant (PDA), a smart phone, or any programmable electronic devicecapable of communicating with LUN 104 via SAN 114. Program 300 is acollection of machine readable instructions and/or data that is used tocreate, manage and control certain software functions that will bediscussed in detail, below, in the Example Embodiment sub-section ofthis Detailed Description section.

Computer 200 is capable of communicating with other storage sub-systemsvia SAN 114. SAN 114 can be, for example, a local area network (LAN), awide area network (WAN) such as the Internet, or a combination of thetwo, and can include wired, wireless, or fiber optic connections. Ingeneral, network 114 can be any combination of connections and protocolsthat will support communications between server and storage sub-systems.

Computer 200 is shown as a block diagram with many double arrows. Thesedouble arrows (no separate reference numerals) represent acommunications fabric, which provides communications between variouscomponents of computer 200. This communications fabric can beimplemented with any architecture designed for passing data and/orcontrol information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system. For example,the communications fabric can be implemented, at least in part, with oneor more buses.

Memory 208 and persistent storage 210 are computer-readable storagemedia. In general, memory 208 can include any suitable volatile ornon-volatile computer-readable storage media. It is further noted that,now and/or in the near future: (i) external device(s) 214 may be able tosupply, some or all, memory for computer 200; and/or (ii) devicesexternal to computer 200 may be able to provide memory for computer 200.

Program 300 is stored in persistent storage 210 for access and/orexecution by one or more of the respective computer processors 204,usually through one or more memories of memory 208. Persistent storage210: (i) is at least more persistent than a signal in transit; (ii)stores the program (including its soft logic and/or data), on a tangiblemedium (such as magnetic or optical domains); and (iii) is substantiallyless persistent than permanent storage. Alternatively, data storage maybe more persistent and/or permanent than the type of storage provided bypersistent storage 210.

Program 300 may include both machine readable and performableinstructions and/or substantive data (that is, the type of data storedin a database). In this particular embodiment, persistent storage 210includes a magnetic hard disk drive. To name some possible variations,persistent storage 210 may include a solid state hard drive, asemiconductor storage device, read-only memory (ROM), erasableprogrammable read-only memory (EPROM), flash memory, or any othercomputer-readable storage media that is capable of storing programinstructions or digital information.

The media used by persistent storage 210 may also be removable. Forexample, a removable hard drive may be used for persistent storage 210.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer-readable storage medium that is also part of persistent storage210.

Communications unit 202, in these examples, provides for communicationswith other data processing systems or devices external to computer 200.In these examples, communications unit 202 includes one or more networkinterface cards, including HBA 306. Communications unit 202 may providecommunications through the use of either or both physical and wirelesscommunications links. Any software modules discussed herein may bedownloaded to a persistent storage device (such as persistent storagedevice 210) through a communications unit (such as communications unit202).

I/O interface set 206 allows for input and output of data with otherdevices that may be connected locally in data communication with servercomputer 200. For example, I/O interface set 206 provides a connectionto external device set 214. External device set 214 will typicallyinclude devices such as a keyboard, keypad, a touch screen, and/or someother suitable input device. External device set 214 can also includeportable computer-readable storage media such as, for example, thumbdrives, portable optical or magnetic disks, and memory cards. Softwareand data used to practice embodiments of the present invention, forexample, program 300, can be stored on such portable computer-readablestorage media. In these embodiments the relevant software may (or maynot) be loaded, in whole or in part, onto persistent storage device 210via I/O interface set 206. I/O interface set 206 also connects in datacommunication with display device 212.

Display device 212 provides a mechanism to display data to a user andmay be, for example, a computer monitor or a smart phone display screen.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

II. Example Embodiment

FIG. 2 shows flowchart 250 depicting a method according to the presentinvention. FIG. 3 shows program 300 for performing at least some of themethod actions of flowchart 250. This method and associated softwarewill now be discussed, over the course of the following paragraphs, withextensive reference to FIG. 2 (for the method action blocks) and FIG. 3(for the software blocks).

At action 255, write request module (“mod”) 355 accepts a request fromfile server computer 200 (see FIG. 1) to write a block of data toLUN/RAID array 104. In this example, the block to be written is datablock 322. As file server computer 200 is connected to RAID array 104via two storage-side interfaces (I/O interfaces 311 and 312), program300 must decide to which interface it will forward the write request.Note that while the device components of file server system 100 are realcomponents in this embodiment, they could alternatively be virtualcomponents, such as is commonly found in cloud environments; there couldbe multiple interfaces on the host side as well as on the storage side;and the LUN and host could be linked by mechanisms other than a SAN,such as in the case of direct-attached storage (DAS).

At action 260, stripe lookup mod 360 determines to which RAID stripedata block 322 belongs and which of I/O interfaces 311 and 312, ifeither, has the parity block for that stripe buffered. Stripe lookup mod360 makes this determination by consulting table 302, which tracks thestripes most recently written by I/O interface (and thus the stripeswhose parity blocks are buffered by that interface). Table 302 currentlycontains only 1 entry—the ordered pair (331, 311)—which specifies thatstripe 331 was recently written to via I/O interface 311. Afterdetermining that block 322 belongs to stripe 331 (for example, byknowing the starting address of block 322 and the starting address andlength of stripe 331), stripe lookup mod 360 consults table 302 todetermine that this stripe was recently written by I/O interface 311.

Note that, in general: (i) any number of interfaces could be supportedon the storage side; (ii) multiple LUNs could be supported by alsotracking LUN in table 302; (iii) multiple HBAs or host-side storageclients sharing the same LUN could be supported, as long as table 302remains in sync across these clients (for example by maintaining table302 in a section of shared memory on a computer hosting all theclients); (iv) parity blocks or other data integrity information neednot all be stored on the same device but could instead be distributedamong the devices (for example, the locations of data block 325 andparity block 326—but not those of data block 322 and parity block323—might be swapped in some embodiments); and/or (v) a stripe may havemultiple parity blocks, as in RAID 6. Note also that I/O interfaces 311and 312 need not be part of LUN 104 but could be, for example,interfaces on the host side, if there is a direct correspondence betweenthose interfaces and the private buffering of RAID parity blocks.

Although the purpose of determining the stripe here is to determinewhere, if at all, the associated parity block is buffered, determiningthe stripe could also be of value where, say, no parity is involved, butattempts to write to the same stripe by different interfacessimultaneously or in rapid succession causes some degree of contention.In such a situation, determining stripe 331 was recently written to viaI/O interface 311 (or that I/O interface 311 has a data block of stipe331 buffered, or some other measure or proxy of the degree of contentionor contention relief) would allow subsequent writes to that same stripeto be routed to the same interface, thereby reducing contention andimproving performance.

At action 265, interface selection mod 365 selects an interface to whichto send the write request. Interface selection mod 365 chooses to sendthe request to I/O interface 311 because this interface was previouslydetermined by stripe lookup mod 360 to have parity block 323 alreadybuffered (see above). This is an example of a stipe-interfacepreference. Had stripe lookup mod 360 not found an interface with parityblock 323 already buffered, interface selection mod 365 would haveselected an interface based on the round robin protocol (alternatelychoosing interface 311, then 312, and so on), though in the fallbackcase where no interface has the necessary parity block buffered, anyselection protocol could be used.

At action 270, table update mod 370 updates the table to account for thelatest write action. Here the update involves only updating the time atwhich the ordered pair (331, 311) was last written, but could alsoinvolve adding and/or deleting entries from the table. For instance, hadtable 302 not contained an entry for stripe 331 and had interfaceselection mod 365 picked interface 311 using the round robin protocol,table update mod 370 would have added the ordered pair (331, 311) totable 302. If the number of entries in table 302 for interface 311 priorto this addition had indicated that buffers for interface 311 werealready full, table 302 would have deleted the oldest entry forinterface 311 prior to adding the ordered pair, mirroring the actioninterface 311 would take to free up buffer space when it receives thelatest write request. In this way, the table remains up to date for thenext table lookup. Note that alternatively or in addition, othermechanisms can be used for keeping the table updated, including updatingthe table responsive to explicit feedback from the interfaces themselvesabout what they are doing with their buffers.

III. Further Comments and/or Embodiments

Some embodiments of the present invention recognize: (i) that whenever ablock is written to a RAID 5 array, it is necessary to recalculate andrewrite the parity block for the stripe the block belongs to; (ii) thatthis process requires that the parity block be transferred into a bufferwhere the parity calculation can be performed and the block's contentsupdated; (iii) that subsequent to these actions, the updated data andparity blocks are written to the respective devices in which theyreside; (iv) that in some storage subsystems, the buffers for the paritycalculation may be private to specific interfaces on the storagesubsystem; and/or (v) that in such storage subsystems, if one block iswritten to a given stripe on one interface, and then another block inthe same stripe is written on another interface, a transfer of theparity block from one buffer to another may be required, causing thesecond write to incur a performance penalty while it waits for thetransfer to take place.

Some embodiments of the present invention recognize: (i) that none ofthe surveyed multipath routing algorithms exploit awareness of the RAIDtopology; (ii) that because of this, these algorithms may write blocksfrom the same RAID stripe to different I/O interfaces; and (iii) thatthis in turn may cause RAID parity blocks to have to be transferredbetween the buffers associated with those interfaces, resulting in aperformance penalty.

As a result, some embodiments of the present invention may include amultipath routing algorithm that: (i) includes awareness of RAIDtopology; (ii) optimizes the case where a block in a RAID stripe hasbeen recently written, and another block in the same RAID stripe isabout to be written; and/or (iii) routes the second write to the sameinterface as the first, reducing the probability of having to transferthe parity block from another interface or read it from non-volatilestorage, both of which would incur a performance penalty.

Shown in FIG. 4 is a multipath RAID system. FIG. 4 depicts input/output(I/O) interface (buffer set) 401 and I/O interface (buffer set) 402 attimes T1, T2, and T3. FIG. 4 also includes: paths 403 and 404; datablocks A 405, B 406, and C 407; and parity block P 408. At time T1, ahost (not shown) writes data block A 405 to I/O interface 401 via path403. (The path chosen is according to a known multi-path routingalgorithm, such as shortest queue or round robin.) Parity block P 408,which is the parity block for the RAID stripe that block A resides in,is read into a buffer associated with I/O interface 401 and updated. Attime T2, the host writes data block B 406, which is in the same RAIDstripe as block A, to I/O interface 402 via path 404. Because parityblock P is currently in a buffer in I/O interface 401, it must betransferred to I/O interface 402; this transfer causes a delay to thecompletion of the block B write operation. At time T3, the host writesblock C 407, which is also in the same RAID stripe as blocks A and B, toI/O interface 401. Because parity block P is buffered at I/O interface402, it must be transferred back to I/O interface 401, which againcauses a delay in the write operation.

Shown in FIG. 5 is a similar sequence of writes, but in aRAID-topology-aware system. FIG. 5 depicts input/output (I/O) interface(buffer set) 501 and I/O interface (buffer set) 502 at times T1, T2, andT3. FIG. 5 also includes: paths 503 and 504; data blocks A 505, B 506,and C 507; and parity block P 508. At time T1, a host (not shown) writesblock A 505 to I/O interface 501 via path 503, and parity block P 508 isread into a buffer on I/O interface 501 and updated, similarly to whatwas described above for FIG. 4. At time T2, however, the host exploitsthe knowledge that block B 506 resides in the same RAID stripe as blockA, and, knowing that parity block P is already buffered at I/O interface501, writes block B to I/O interface 501, updating the parity blockaccordingly. Note that, unlike in FIG. 4, no transfer of the parityblock is required. Finally, at time T3, the host exploits the knowledgethat block C 507 resides in the same RAID stripe as blocks A and B, andwrites block C to I/O interface 501. Again, parity block P is updatedwithout it having to be transferred from another interface. In total,two transfers of a parity block were avoided in the example of FIG. 5relative to the example of FIG. 4.

In some embodiments of the present invention, a table is maintained inthe host. The table contains one entry for each RAID buffer associatedwith an interface on the storage subsystem. Each entry contains the LUN(logical unit number), starting logical block address, and length of astripe that was recently written to that interface. When a write I/O isissued, the host checks to see if the block to be written belongs to astripe in the table. If it does, it sends the I/O down a path to theinterface associated with that table entry. If it does not, it uses afallback algorithm to choose the path.

In some embodiments of the present invention, entries in the table aremanaged in the same way as buffers in the storage subsystem. Forexample, if buffers in the storage subsystem are managed using an LRU(least recently used) replacement algorithm, then entries in the tableare also managed using an LRU algorithm so that the parity blocksbuffered in the storage subsystem correspond to the entries in thehost's table.

In some embodiments of the present invention, a more deterministicscheme is used that entails having the storage subsystem provideinformation to the host on the stripes for which it has the parityblocks buffered. This information is stored directly in a host table,keeping the entries in the table in sync with the buffered parityblocks.

Some embodiments of the present invention include one or more of thefollowing features, characteristics, or advantages: (i) apply aRAID-topology-aware algorithm to a RAID 5 storage system; (ii) apply aRAID-topology-aware algorithm to any RAID topology where a paritycalculation is applied to a set of blocks with a known topology (RAID 6,for example); (iii) use one or more tables or other associativemechanisms to track blocks, the stripe to which they belong, and theinterface over which that stripe was most recently written; (iv)maintain the table(s) or other associative mechanism(s) at the host orat some other point in the storage system such that the associativeinformation is accessible when selecting an interface from multiplepossible interfaces to a storage device; (v) achieve performanceimprovements in storage subsystems where RAID parity buffers are privateto each interface; and/or (vi) achieve performance improvements instorage subsystems where performance is enhanced by sending a write tothe same interface where a write in the same RAID stripe has beenrecently sent (for example, in a storage subsystem where performancedegradation due to contention occurs if two or more writes to the samestripe are sent through more than one interface).

IV. Definitions

Present invention: should not be taken as an absolute indication thatthe subject matter described by the term “present invention” is coveredby either the claims as they are filed, or by the claims that mayeventually issue after patent prosecution; while the term “presentinvention” is used to help the reader to get a general feel for whichdisclosures herein are believed to potentially be new, thisunderstanding, as indicated by use of the term “present invention,” istentative and provisional and subject to change over the course ofpatent prosecution as relevant information is developed and as theclaims are potentially amended.

Embodiment: see definition of “present invention” above—similar cautionsapply to the term “embodiment.”

and/or: inclusive or; for example, A, B “and/or” C means that at leastone of A or B or C is true and applicable.

Including/include/includes: unless otherwise explicitly noted, means“including but not necessarily limited to.”

Module/Sub-Module: any set of hardware, firmware and/or software thatoperatively works to do some kind of function, without regard to whetherthe module is: (i) in a single local proximity; (ii) distributed over awide area; (iii) in a single proximity within a larger piece of softwarecode; (iv) located within a single piece of software code; (v) locatedin a single storage device, memory or medium; (vi) mechanicallyconnected; (vii) electrically connected; and/or (viii) connected in datacommunication.

Computer: any device with significant data processing and/or machinereadable instruction reading capabilities including, but not limited to:desktop computers, mainframe computers, laptop computers,field-programmable gate array (FPGA) based devices, smart phones,personal digital assistants (PDAs), body-mounted or inserted computers,embedded device style computers, application-specific integrated circuit(ASIC) based devices.

Data stripe: a set of logically sequential data segments, such thatconsecutive segments are stored on different physical and/or virtualstorage devices; may or may not include data integrity informationrelated to the data segments of the stripe.

Block: as used herein, a segment of a data stripe stored on a physicalor virtual storage device distinct from the device(s) storing othersegments of that stripe; a bit, a byte, or a multi-byte segment are allexamples of blocks (depending, for example, on the RAID level beingreferenced).

What is claimed is:
 1. A method for use with a redundant array ofindependent disks (RAID) data storage system that includes a pluralityof storage system interfaces and that stores data organized into aplurality of RAID stripes, the method comprising: receiving a consultingtable associated with a set of input data, with the set of input dataincluding information indicative of, for each given RAID stripe of theplurality of RAID stripes, an identification of a corresponding storagesystem interface of the plurality of storage system interfaces that wasmost recently used to save data to the given RAID stripe; receiving afirst request for storing a first piece of data to a first RAID stripeof the plurality of RAID stripes; responsive to receipt of the firstrequest, determining, based on the input data included in the consultingtable, that a first storage system interface, of the plurality ofstorage system interfaces, was most recently used to save data to thefirst RAID stripe; and responsive to the determination that that thefirst storage system interface was most recently used to save data tothe first RAID stripe, routing the first piece of data through the firststorage system interface to thereby save the first piece of data on thefirst RAID stripe of the RAID data storage system.
 2. The method ofclaim 1 further comprising: buffering, in the first storage systeminterface, data relating to the first RAID stripe; and determining,based at least in part upon the determination that the first storagesystem interface was most recently used to save data to the first RAIDstripe, that the first RAID stripe has an associated parity block forthe buffered data relating to the first RAID stripe.
 3. The method ofclaim 1 wherein: the consulting table includes one data entry for eachbuffered data of a given RAID stripe.
 4. The method of claim 1 wherein:each entry of the consulting table includes information indicative of:(i) a logical unit number (LUN); (ii) a starting logical block address;and/or (iii) a length of a RAID stripe that was recently written to aninterface.
 5. The method of claim 1 wherein each entry of the consultingtable is managed using a Least Recently Used (LRU) algorithm.
 6. Themethod of claim 5 wherein buffered data associated with a given parityblock in the first storage system corresponds to an entry in theconsulting table.
 7. A computer program product for use with a redundantarray of independent disks (RAID) data storage system that includes aplurality of storage system interfaces and that stores data organizedinto a plurality of RAID stripes, the computer program productcomprising: a machine readable storage device; and computer code storedon the machine readable storage device, with the computer code includinginstructions and data for causing a processor(s) set to performoperations including the following: receiving a consulting tableassociated with a set of input data, with the set of input dataincluding information indicative of, for each given RAID stripe of theplurality of RAID stripes, an identification of a corresponding storagesystem interface of the plurality of storage system interfaces that wasmost recently used to save data to the given RAID stripe, receiving afirst request for storing a first piece of data to a first RAID stripeof the plurality of RAID stripes, responsive to receipt of the firstrequest, determining, based on the input data included in the consultingtable, that a first storage system interface, of the plurality ofstorage system interfaces, was most recently used to save data to thefirst RAID stripe, and responsive to the determination that that thefirst storage system interface was most recently used to save data tothe first RAID stripe, routing the first piece of data through the firststorage system interface to thereby save the first piece of data on thefirst RAID stripe of the RAID data storage system.
 8. The product ofclaim 7 further comprising: buffering, in the first storage systeminterface, data relating to the first RAID stripe; and determining,based at least in part upon the determination that the first storagesystem interface was most recently used to save data to the first RAIDstripe, that the first RAID stripe has an associated parity block forthe buffered data relating to the first RAID stripe.
 9. The product ofclaim 7 wherein: the consulting table includes one data entry for eachbuffered data of a given RAID stripe.
 10. The product of claim 7wherein: each entry of the consulting table includes informationindicative of: (i) a logical unit number (LUN); (ii) a starting logicalblock address; and/or (iii) a length of a RAID stripe that was recentlywritten to an interface.
 11. The product of claim 7 wherein each entryof the consulting table is managed using a Least Recently Used (LRU)algorithm.
 12. The product of claim 11 wherein buffered data associatedwith a given parity block in the first storage system corresponds to anentry in the consulting table.
 13. A computer system for use with aredundant array of independent disks (RAID) data storage system thatincludes a plurality of storage system interfaces and that stores dataorganized into a plurality of RAID stripes, the computer systemcomprising: a processor(s) set; a machine readable storage device; andcomputer code stored on the machine readable storage device, with thecomputer code including instructions and data for causing theprocessor(s) set to perform operations including the following:receiving a consulting table associated with a set of input data, withthe set of input data including information indicative of, for eachgiven RAID stripe of the plurality of RAID stripes, an identification ofa corresponding storage system interface of the plurality of storagesystem interfaces that was most recently used to save data to the givenRAID stripe, receiving a first request for storing a first piece of datato a first RAID stripe of the plurality of RAID stripes, responsive toreceipt of the first request, determining, based on the input dataincluded in the consulting table, that a first storage system interface,of the plurality of storage system interfaces, was most recently used tosave data to the first RAID stripe, and responsive to the determinationthat that the first storage system interface was most recently used tosave data to the first RAID stripe, routing the first piece of datathrough the first storage system interface to thereby save the firstpiece of data on the first RAID stripe of the RAID data storage system.14. The system of claim 13 further comprising: buffering, in the firststorage system interface, data relating to the first RAID stripe; anddetermining, based at least in part upon the determination that thefirst storage system interface was most recently used to save data tothe first RAID stripe, that the first RAID stripe has an associatedparity block for the buffered data relating to the first RAID stripe.15. The system of claim 13 wherein: the consulting table includes onedata entry for each buffered data of a given RAID stripe.
 16. The systemof claim 13 wherein: each entry of the consulting table includesinformation indicative of: (i) a logical unit number (LUN); (ii) astarting logical block address; and/or (iii) a length of a RAID stripethat was recently written to an interface.
 17. The system of claim 13wherein each entry of the consulting table is managed using a LeastRecently Used (LRU) algorithm.
 18. The system of claim 17 whereinbuffered data associated with a given parity block in the first storagesystem corresponds to an entry in the consulting table.